In the axion-like dark matter searches (Secs.  and ), we focus on the search via the axion-nucleon interactions known as `the axion gradient effect' [1]}, [2]}, [3]}, [4]}, [5]}, [6]}, [7]} (see Sec. REF ). In this model, axion-like dark matter acts as a time-oscillating magnetic field which couples to nuclear spins. Through spin-based amplifier, the effect of axion-like field can be enhanced and the measurement sensitivity can be greatly improved.
